1. Field of the Invention
The subject invention relates to a composite article and a method of forming the same, and specifically, to a composite article having improved adhesion between layers.
2. Description of the Related Art
Bowling balls can be comprised of a core and a cover stock surrounding the core. Additional layers or components may be present in the core resulting in an inner and outer core to vary different properties of the bowling ball, mainly performance. The inner core is typically a center weight within the bowling ball and may be formed of various materials. The inner core may not be spherical and is shaped to enhance performance by effecting the precession or flare of the bowling ball. As understood by those of ordinary skill in the art, these performance weights can be, but not limited to being, oblong, boomerang shaped, dog bone shaped, etc. The outer core is the layer between the inner core and the cover stock and provides a spherical core. The coverstock is the outer-most shell of the bowling ball. There are different types of materials that may form the coverstock, such as, polyester and polyurethane compositions.
The type of material forming the cover stock is selected depending upon the desired reactivity of the bowling ball when rolled and the desired on-lane performance. For example, cover stocks formed of polyester are very durable and hard, but the polyester cover stocks have low friction on oiled lane surfaces. This low friction causes the bowling ball to skid more and maintain a straighter trajectory when rolled, i.e., less hook is achieved. Polyurethane cover stocks, on the other hand, tend to be softer, have different polymer morphology compared to polyester balls and have higher friction. The higher friction can cause the bowling ball to be more reactive on the bowling lane and perform better. Additional additives may be added to the polyurethane coverstock to provide different levels of texture and effective friction, such as resins, ceramics, or glass particles.
Polyurethane materials have been used for bowling ball coverstocks for many years. Polyurethane materials are used industry-wide for professional bowling balls (and high-end amateur products) because they provide the necessary on-lane performance desired at the higher levels of play.
The polyurethane materials of the related art generally comprise the reaction product of a polyol and a polyisocyanate forming cross-linkages with the polyol and having a non-reactive diluent dispersed within the matrix. The non-reactive diluent is typically a plasticizer and is one of the most important elements contributing to ball reactivity. Plasticizers such as 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (Kodaflex “TXIB”), from Eastman Chemical Company, are used in such polyurethane elastomeric materials.
Typically, bowling ball cores can be constructed using various materials. The most common materials are unsaturated polyesters, especially, styrenated polyesters. Advances in core designs have resulted in the development of a round core that is constructed from an inner geometric shape, or inner core, and a shell cast around this inner core forming an outer core. The outer core must be prepared using materials that adhere well to the cover stock. Most bowling balls are drilled with holes to fit a user's hand and fingers. When the bowling ball is drilled, the interface between the outer core and the cover stock undergoes increased stresses. If the cover stock and outer core are not sufficiently adhered to one another, the bowling ball core can separate from the cover stock and/or crack between the finger holes. Still another issue present in the related art is that the outer core has a tendency to shrink over time after production, which further increases the stresses at the interface between the outer core and the cover stock.
The use of hydroxyethyl methacrylate (HEMA) as an adhesion promoter is well known. U.S. Pat. Nos. 5,639,546 and 6,509,086 disclose the use of HEMA to promote adhesion in composite articles. However, the '546 patent requires a radical curing process and is unlikely to form a thin film. Moreover, the polyethylenically unsaturated monomers form a cured layer that promotes adhesion when cured with a photoinitiator. The '086 patent discloses a system that incorporates a urethane acrylate as an additive to the acrylate layer. The result of such a system is two similar polymer layers that do not have dual adhesive and cohesive forces interacting between the layers.
Most related art systems wipe or spray the adhesion promoter directly onto the first layer prior to casting the second layer. Such an additional step results in additional time required in manufacturing, potentially exposing employees to added chemical exposure hazards, and there questions whether there is adequate assurances that the adhesion promoter has sufficiently bonded with the first layer prior to casting the second layer.